Conventionally, light-emitting devices which emits light having a different color from the emission color of a LED chip by combining the LED chip and a phosphor (e.g., fluorescent pigment and fluorescence dye) as a wavelength converting material which emits light having an emission color different from that of the LED chip when excited by the light emitted by the LED chip have been researched and developed at various places. Such light-emitting devices include a commercialized white light-emitting device (which is generally called a white LED) in which an LED chip for emitting blue light or ultraviolet light is combined with a phosphor to produce a white light (emission spectrum of white light).
Also, the application of white LEDs to a luminaire has become an active area for research and development in accordance with recent high output of white LEDs, but when the white LED is applied to an application which requires a relatively high light output such as general illumination, a desired light output cannot be produced by only one white LED. So, generally, a plurality of white LEDs are mounted on one circuit board to form an LED unit (light-emitting device), and the LED unit ensures the desired light output as a whole (for example, see Japanese Patent Application Laid-Open No. 2003-59332 (hereinafter, referred to as Patent Document 1)).
Also, conventionally, in the light-emitting device having an LED chip and a circuit board on which the LED chip is mounted, a structure for effectively dissipating heat generated in a light-emitting part of the LED chip to the outside has been proposed so as to increase the power of the light output by constraining a rise of a junction temperature of the LED chip and increasing the input power (for example, see Japanese Patent Application Laid-Open No. 2003-168829 (hereinafter, referred to as Patent Document 2), Paragraph[0030] and FIG. 6).
In the light-emitting device disclosed in Patent Document 2, as shown in FIG. 12, a metal substrate in which a conductor pattern 203 is formed via an insulating resin layer 202 on a metal plate 201 is adopted as a circuit board 200 on which LED chips 10′ are mounted, so that the heat generated at each of the LED chips 10′ can be transferred to the metal plate 201 through a heat transfer member 210. In this case, each of the LED chips 10′ is a GaN-based blue LED chip in which a light-emitting part made of a GaN-based compound semiconductor material is formed on one surface side of a substrate for crystal growth formed from a sapphire substrate which is an insulator, and each LED chip 10′ is mounted on the circuit board 200 by flip chip, and the other surface of the substrate for crystal growth is a light output surface.
When the light-emitting device having a configuration shown in FIG. 12 is applied to a luminaire, in order to efficiently dissipate heat generated in the light-emitting device, it is conceivable that the body of the luminaire for holding the circuit board 200 on which the LED chips 10′ are mounted is made of a metal, and the metal plate 201 of the circuit board 200 of the light-emitting device is thermally connected to the metal body of the luminaire. However, in order to ensure a lighting surge protection, it is necessary to interpose a heat radiation sheet having a rubber sheet shape, such as Sarcon (registered trademark), as a sheet-shaped insulating layer, between the body of the luminaire and the metal plate 201 of the circuit board 200, so the heat resistance from the light-emitting part of each LED chip 10′ to the body of the luminaire, which is the metal member, for holding the light-emitting device is increased. Therefore, it is necessary to limit the input power to each LED chip 10′ to prevent the junction temperature of each LED chip 10′ from rising above the maximum junction temperature, so it is difficult to increase the power of the light output.
In addition, when the above-mentioned heat radiation sheet is interposed between the metal plate 201 and the body of the luminaire, the heat radiation sheet may cause lack of adhesion between the metal plate 201 and the heat radiation sheet, which may lead to an increased heat resistance due to air spaces generated between the sheet and the plate, or which may lead to various heat resistances between each of the light-emitting devices and the body of the luminaire.
Furthermore, in the light-emitting device disclosed in Patent Document 2, since the heat generated in the light-emitting part of the LED chip 10′ is transferred to the metal plate 201 via the heat transfer member 210 having a size smaller than that of the LED chip 10′, the heat resistance from the LED chip 10′ to the metal plate 201 is relatively high. Therefore, when the sapphire substrate, that is the substrate for crystal growth, is mounted on the metal plate 201 to be thermally connected, there is a problem that the heat resistance of the sapphire substrate is increased.